N-phosphonomethylglycine [PO(OH)2CH2NHCH2COOH], which is commonly referred to as glyphosate acid or simply glyphosate, is well known in the art as a highly effective herbicide. It is also known that glyphosate, an organic acid, has relatively low solubility in water. Thus, glyphosate is typically formulated as a water-soluble salt, particularly as the mono-isopropylamine (IPA) salt, to kill or control weeds or plants. Glyphosate salt is sold commercially as an aqueous concentrate or dry salt by Monsanto Company of St. Louis, Mo. (U.S.A.) under the registered trademark ROUNDUP.
Various salts of glyphosate, methods for preparing salts of glyphosate, formulations of glyphosate and methods of use for killing and controlling weeds and plants are disclosed in U.S. Pat. Nos. 3,799,758 and 4,405,531 issued to John E. Franz. Other U.S. Patents which disclose salts of glyphosate include U.S. Pat. No. 4,315,765 issued to George B. Large, U.S. Pat. Nos. 4,507,250 and 4,397,676 issued to Izak Bakel, U.S. Pat. No. 4,481,026 issued to Michael P. Prisbylla and U.S. Pat. No. 4,140,513 issued to Erhard J. Prill. All of the foregoing patents, in their entireties, are incorporated herein by reference.
ROUNDUP brand herbicide is sold as a water-soluble liquid concentrate. However, efforts have recently been made in the art to develop water-soluble dry/solid glyphosate formulations which have the equivalent efficacy of ROUNDUP. Conventional reasons underlying these efforts have been desired cost savings in connection with the packaging, shipment and storage of a solid formulation versus a liquid. As can be appreciated, aqueous concentrates include a significant amount of water that adds to the size and weight of packaging containers and increases costs associated with post-manufacture delivery of the product to market. Less readily apparent benefits of making a dry, water-soluble glyphosate formulation, such as a granular formulation, include superior handling characteristics (e.g., controlled spillage) and the expectation that such formulations will be substantially lighter and less awkward to transport (and often hand carry) thereby making the product better suited for use in remote geographic locations.
Making a dry glyphosate formulation, however, entails overcoming inherent disadvantages relating principally to the increased production cost and comparative complexity of compounding a solid product from a combination of liquid and solid components rather than making a product in solution from the same components.
Several methods for making a solid, water-soluble, glyphosate salt-containing composition are known. For example, U.S. Pat. No. 5,047,079 issued to Djafar discloses a method for preparing a phytotoxic composition comprising admixing highly hygroscopic isopropylamine salt of glyphosate acid with a molten surfactant to form a matrix, the surfactant being a solid at ambient temperatures.
U.S. Pat. No. 5,070,197 issued to Chin, et. al. discloses an extrusion method in which a Bronsted acid, N-phosphonomethylglycine for example, is intimately admixed with a base, sodium hydroxide for example, in an extruder to produce a granular extrudate having a residual moisture content of no greater than 10%. Another method involving the production of a dry sodium glyphosate composition, albeit not involving extrusion, is disclosed in PCT application Publication No. WO 87/04595.
U.S. Pat. No. 5,266,553 issued to Champion, et al. discloses a process for preparing a dry water-soluble salt of a herbicide having a carboxylic acid functionality wherein a solution or slurry of the salt is prepared by reacting the herbicide in acid form with a sufficient amount of a neutralizing base in the presence of water to neutralize the herbicide by about 98 to about 100 mole percent and the solution or slurry is then dried. The process is primarily directed to ammonium and alkylammonium salts of substituted benzoic acid and phenoxy-substituted carboxylic acid herbicides, but the process is said to be useful also for salts of glyphosate.
In French Patent Publication No. 2.692.439 assigned to Productos Osa SACIFIA, there is generally described a phytotoxic preparation comprising the mono-ammonium salt of N-phosphonomethylglycine as a powder or granule in combination with a wetting agent, surfactant and/or a pulverulent additive. As exemplified in the reference, the mono-ammonium salt is derived from reacting glyphosate acid with ammonium bicarbonate.
U.S. Pat. No. 5,324,708 issued to Moreno, et. al. discloses a composition and related methods for preparing and using a non-hygroscopic mono-ammonium glyphosate salt such as the mono-isopropylammonium salt of N-phosphonomethylglycine and the mono-isopropylammonium salt of (3-amino-3-carboxypropyl)-methane phosphonic acid in dry powder form.
PCT application Publication No. WO 94/10844 discloses a dry glyphosate composition in which N-phosphonomethylglycine is admixed with, inter alia, an inorganic or organic, non-caustic base material such as di-ammonium phosphate or a basic guanidine salt such as guanidinium acetate.
EPO application Publication No. 0 394 211 discloses an invention comprising a dry pesticidal composition and related methods for use and production. More particularly, the invention relates to the enhanced solubility of the pesticidal composition as achieved by the addition of an effective amount of an organosilicone block copolymer or a fluorocarbon wetting agent.
PCT application Publication No. WO 90/07275 discloses an invention by which granular, water-soluble glyphosate compositions are made as by admixing, pan granulation, drying, spraying and extrusion.
PCT application Publication No. WO 92/12637 discloses water-soluble tablets containing glyphosate acid, an acid acceptor such as sodium oxalate, and an optional anionic surfactant. The acid acceptor is said to solubilize glyphosate acid through glyphosate salt formation upon exposure to water.
PCT application Publication No. WO 01/08492 discloses, a process for preparing a dry granular herbicidal composition, comprising forming an ammonium glyphosate paste by mixing in a suitable vessel particulate glyphosate acid, ammonia in an amount of about 0.8 to about 1.25 moles per mole of the glyphosate acid, and water in an amount of about 10% to about 25% by weight of all materials being mixed in the vessel, thereby causing a reaction of the glyphosate acid and ammonia that generates heat causing partial evaporation of the water, and forms the ammonium glyphosate paste having a moisture content of about 5% to about 20% by weight. If the moisture content of the paste is greater than about 15% by weight, heat and/or vacuum is applied to reduce the moisture content to about 5% to about 15% by weight. Thereafter, one or more surfactants are added to the paste, with mixing, in a weight ratio of total surfactant to ammonium glyphosate of about 1:9 to about 1:3 to form an extrudable wet mix. The wet mix is extruded to form extrudate strands that break to form moist coherent granules that are dried to produce the dry granular composition.
U.S. Pat. No. 6,599,858 issued to Kramer discloses, a process for preparing ammonium glyphosate flakes, comprising mixing solid particulate glyphosate acid, water in an amount of about 0.5 to about 3 parts by weight of glyphosate acid and a base that supplies ammonium cations to form an aqueous reaction medium. The glyphosate acid reacts with the base to form a concentrated aqueous solution of which is further processed to form dry flakes of ammonium glyphosate.
U.S. Pat. No. 6,448,434 issued to Kramer discloses, a process for preparing ammonium glyphosate flakes, comprising mixing solid particulate glyphosate acid, water in an amount of about 0.5 to about 3 parts by weight of glyphosate acid and a base that supplies ammonium cations to form an aqueous reaction medium. The glyphosate acid reacts with the base to form a concentrated aqueous solution of which is then dried to form a particulate solid ammonium glyphosate. The particulate solid ammonium glyphosate is jet milled to form a powder ammonium glyphosate.